Fukushima Factors

Situation at the Fukushima Daiichi nuclear power plant: panel of speakers sits at long table with screen behind them
From left to right: Hidehiko Yamachika, Michael Podowski, Rebecca Bittner, Margaret Harding, Majid Manzari and Philippe Bardet.
May 05, 2011

By Laura Donnelly-Smith

Japan’s Fukushima Daiichi nuclear power plant weathered the March 11 earthquake remarkably well given its age, but it was the catastrophic tsunami that followed that caused several reactors’ cooling systems to suffer critical damage.

That was the opinion of a panel of nuclear energy experts from Japan and the United States, who gathered Tuesday in GW’s Jack Morton Auditorium to discuss the situation at the Fukushima Daiichi reactor. The panel was convened and moderated by GW Assistant Professor of Mechanical and Aerospace Engineering Philippe Bardet, who said he felt frustrated by some of the media’s uninformed accounts of the plant disaster and the public’s subsequent misunderstanding of what was taking place in Fukushima Daiichi.

Dr. Bardet explained how, in March, he read news coverage stating that the Fukushima reactors were poorly designed, and that design flaws were the reason the reactors overheated. “That’s not factually correct—it was opinion, but it was presented as fact. I wish they would have run the article by an engineer to check the accuracy,” he said. “People can become very emotional when talking about nuclear energy, and they can lose reason as emotion kicks in.”

The panel, which included GW Professor of Civil and Environmental Engineering Majid Manzari, reactor safety expert Margaret Harding, Japan Nuclear Energy Safety Organization General Manager Hidehiko Yamachika, GW Assistant Professor of Radiology Rebecca Bittner, and Rensselaer Polytechnic Institute Professor of Nuclear Engineering Michael Podowski, presented information on the sequence of events in the disaster, the plant’s design and safety, the human health risks that come with radiation exposure and how future nuclear disasters may be prevented using emerging technologies, newer plant designs and better detection of earthquakes before they cause tsunami waves.

Dr. Manzari explained that the 9.0-magnitude earthquake was caused by two tectonic plates—the Pacific plate and the Eurasian plate—moving on the earth’s surface. When such movement takes place without obstruction, everything is fine. But in March, the edge of the Pacific plate met resistance under the Eurasian plate, got stuck and caused energy to build up. The stuck area eventually ruptured, causing the earthquake and resulting tsunami. The amount of energy released, Dr. Manzari said, caused the island of Japan to migrate 2.4 meters, and was large enough to power the city of Los Angeles for an entire year.

Ms. Harding, a former vice president at GE Nuclear Energy and a current consultant to the nuclear industry on regulatory issues, described in layman’s terms the features of the Fukushima plant and how it worked. The plant put its reactors—boiling water reactors, or BWRs—online between 1971 and 1974. “Because the water in the reactor actually boils, you have steam spinning a turbine. It’s a really high-tech teapot that makes electricity,” Ms. Harding explained. Fuel sits in a 40-foot-deep pool of water, which both cools the heated fuel and protects plant workers from radiation.

Mr. Yamachicka explained the sequence of events affecting the reactors in the aftermath of the earthquake, and Dr. Podowski talked about the passive safety systems built into second-generation BWRs like Fukushima Daiichi. These include core isolation systems, high-pressure emergency cooling systems and overpressurization preventers.

“All of these systems worked in Japan,” Dr. Podowski said. “The biggest issue in the Japanese accident was that [cooling] water was being pumped into the system, but initially there was no way to remove it in a safe manner, so it didn’t end up in the ocean but could be cooled and returned to the system.”

The Fukushima Daiichi plant was designed to withstand an 8.5-magnitude earthquake and a 5-meter-high tsunami, and it performed admirably, he said. But the 9.0-magnitude earthquake and 14-meter resulting tsunami overwhelmed the plant.

“This earthquake was strong, but the reactors survived very well,” Dr. Podowski said. “The damage was severe due to the tsunami. Even when power was restored, time was needed to start injecting water to cool the reactors. The lesson learned is that you have to anticipate what nature can do to us.”

Japan’s ability to deal with the nuclear reactor crisis was also affected by the overwhelming devastation in so much of the area, he said. In most situations, there would be more people to call for help—first responders as well as nuclear crisis experts. In Japan in March, no one was there because the damage was so absolute and widespread.

Dr. Bittner discussed health risks related to radiation exposure at the plant, but emphasized that most Japanese citizens would not be exposed to dangerous levels of radiation. Radiation effects depend on a number of factors, she said: the type of radiation, the total dose, how it’s received (one large dose or many smaller ones), the dose rate (slow or fast), the biologic system involved (like skin, bone marrow or gastrointestinal tract), and the method of exposure.

The worst effects come from large, intense doses of radiation, such as those suffered by workers in the Chernobyl reactor room, Dr. Bittner said. In Japan, most citizens needed to be concerned more about smaller amounts of external contamination (such as from living downwind of the plant when radioactive steam escapes) and internal contamination (including ingestion of radioactive material through food and water).

Both types of exposure can be mitigated, she said, by removing clothing worn during exposure and washing the skin well, and by taking care not to eat or drink food or water from near the site. And Dr. Bittner said current data show that even Fukushima plant workers are still well under the radiation exposure limits that would cause acute radiation syndrome, a serious illness.

Looking forward, the panelists agreed that better earthquake prediction will help prevent nuclear disasters in the future, giving plant workers more time to shut reactors down. Newer plant designs—some still many decades away—may also include systems that can run without human intervention for up to three days to cool reactors while emergency workers regroup and set up auxiliary power.

In the United States, it’s unlikely that a situation similar to the Fukushima Daiichi crisis would occur, Dr. Bardet said, because our nuclear plants were built later than the Japanese plants—which were designed in the 1950s and ’60s. “Reactors in the United States are about 2,000 times safer than the older Japanese type,” he said. Still, panelists expressed satisfaction at how the old Japanese reactors at Fukushima Daiichi performed under crisis.

“The engineering of these [reactors] is fantastic,” Dr. Manzari said. “If you look back to what they knew in 1969, it was so elementary compared with today. The design was so good to be able to withstand what it did.”

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